Downhole directional drilling assembly

ABSTRACT

The assembly comprise a bent sub ( 1411 ), and optionally a swivel ( 1480 ). The bend angle a of the bent sub in relation to the central axis of the assembly can be adjusted by rotating lower bend member ( 1431 ) relative to upper bend member ( 1430 ), which is non-rotatably attached to downhole motor ( 1460 ), using harmonic drive ( 1413 ) arranged between lower and upper bend members. In order to adjust the rotational orientation of the bent sub ( 1411 ), a swivel ( 1480 ) is provided having upper and lower swivel members ( 1432, 1433 ). Upper swivel member can be rotated relative to lower member, which is non-rotatably attached to the downhole motor, using a second harmonic drive ( 1423 ) arranged between lower and upper swivel members.

The present invention relates to the field of oil and gas exploration,and in particular downhole activities, such as, for example, drilling,logging, fishing, completions, etc. More specifically, the presentinvention is a drive arrangement suitable for various uses, such as, forexample, driving a component of a Bottom Hole Assembly (BHA) including,but not limited to, a directional drilling tool.

When drilling wellbores for oil and gas production, a drill-string isused which includes various components, such as the drill-bit, BHA and,in some cases, a drill-pipe rotatable by a topmotor at surface which inturn rotates the BHA, typically, during straight drilling. In othercases, coiled tubing is used, a continuous length of pipe wound on aspool which, typically, cannot rotate about its own axis. A work-stringis used within a completed or nearly completed well-bore and includes atubing string used to convey a treatment or equipment for well serviceactivities. Components of these and similar arrangements for downholeactivities may be required to rotate around a central axis. Thedrill-bit, for example, must usually rotate in order that it abrades theseabed to form the well-bore. The rotation may be the whole of thearrangement or it may be the case, for example, where coiled tubing isused, that the arrangement provides for rotation of only part of thework or a drill-string, or that different sections rotate independently,at different angular velocities and/or with different torques beingexerted, or it may be advantageous that only part of the work or adrill-string rotates.

In directional drilling, the BHA typically includes a bent portion nearthe drill bit. Such a BHA typically includes a bent portion or a bentsub. The bent portion points in a direction slightly different from theaxis of the rest of the drillstring including the drill bit. In order toallow the bit to drill in the direction the bent portion points, thedrill bit is rotated, typically, by a downhole motor located within theBHA, while the drillstring above the bit and the bent portion do notrotate. The downhole motor is typically a mud motor, also referred to asa Positive Displacement Motor (PDM), driven by the flow of mud insidethe drillstring.

In drill pipe drilling, where the drill pipe is rotatable by a topmotorat surface, once a particular wellbore direction has been achieved, theentire drillstring, including the drill pipe and the bent portion arerotated as one piece from surface. This allows the drilling to continuealong a straight path with greater speed and torque because therotations of the mud motor and the topmotor add at the drill bit. Therotation of the bent portion results in a slight enlargement of thewellbore diameter. However, since the bend angle between the drillstringaxis and the axis of the bent portion typically lies in the regionbetween 0°-3° and the bent portion is located close to the bit, such anenlargement is negligibly small. When a change in direction is required,the drill string can be rotated slowly to point the bent portion in therequired direction downhole.

In conventional coiled tubing directional drilling, the coiled tubingcannot be rotated and thus it is generally not possible to obtain astraight wellbore while drilling with a bent sub. A straight drillingdirection is typically achieved by alternately drilling in one directionfirst, then orienting the bent portion, e.g. by using a mud flow drivenactuator, to point in opposite direction and then drilling in the seconddirection. Such drilling results in a wavy wellbore which generallyfollows a straight line.

A number of problems exist related to relative rotation of drillstringor workstring components downhole.

One problem associated with the use of a bent sub, regardless whetherdrill pipe or coiled tubing is used, is that adjustment of the angle ofthe bend, and consequently, the amount of deviation of the drillingdirection from a straight path, invariably must be carried out manuallyat the surface. This means that the drilling process needs to be stoppedand the entire drillstring must be pulled out to the surface and theninserted back into the wellbore. In an arrangement described in U.S.Pat. No. 4,836,303, the bend angle can be remotely adjusted downhole,thereby avoiding the need for the drillstring to be recovered to thesurface for adjustment of the bend. However, the drilling operationstill has to be halted and the drillstring lifted off-bottom in orderfor the orientation of the bent sub to be adjusted, thereby stillinvolving a significant amount of non-drilling time (NDT) in anydrilling operation. Furthermore, starting and stopping the drillingoperation can result in a stuck pipe. Moreover, stopping and startingcirculation of the drilling fluid, which interrupts the removal ofcuttings and the cleaning of the borehole, can increase the risk ofstuck pipe occurrence.

Another problem associated with the use of a bent sub in directionaldrilling is caused by the fact that that during directional drilling,the drill bit is rotated downhole by the mud motor whereas thedrillstring including the bent sub above the bit do not rotate. Thedrillstring and the bent sub thus slide in the wellbore as the drill bitis advancing in the direction determined by the bent sub.Slide-drilling, along with low rate of penetration, also brings alongfriction problems between the drillstring and the wellbore walls,including the risk of a stuck drillstring. US 2004/0079552 attempted toaddress this problem in drill pipe drilling by providing a BHA with anoffsetting arrangement to provide a deviation from a straight path andby connecting the drill pipe directly to the bit, dispensing with theneed for a mud motor. This allows the drill pipe to rotate duringdirectional drilling, while the BHA housing does not rotate. However,this is achieved at the expense of not being able to drill along astraight path. Furthermore, this arrangement is inherently not suitablefor coiled tubing drilling. And yet furthermore, the bend angle stillhas to be set at surface.

A further problem in directional drilling, whether using drill pipe orcoiled tubing, is caused by reactive torque created by the drillingfluid hitting against the stator (which is typically the motor housing)of the downhole motor. Since the stator constitutes the body of themotor and comprises part of the BHA housing, the reactive torque twiststhe motor together with the BHA anticlockwise. The reactive torque atthe motor housing is equal to the active drilling torque at the bit.Reactive torque causes a problem during directional drilling because thetwisting of the BHA caused by reactive torque changes the toolfaceorientation of the bent sub over time. Reactive torque which exceeds acertain threshold (over torque) is dangerous as the twisting of thedrillstring results in stresses which can lead to damage or sticking ofthe drillstring. Furthermore, sticking of drillstring causes highlyvariable RPM and drillstring torque transmitted to the BHA. This torqueis reacted by the BHA, which can result in difficulty in maintainingdrilling direction in directional and horizontal wells.

A still further problem associated with drill pipe drilling is thatrotation of the drill pipe can result in drill string components,including the BHA experiencing excessive torque from surface rotation,which can be damaging to the drill string joints and the components ofthe BHA.

Some further examples of downhole activities where rotating componentsare involved and where problems exist related to aspects of relativerotation of components of downhole tools include:

-   -   Wellbore cleaning while drilling    -   Enhanced Rotary Steerable Systems (RSS)    -   Stick slip mitigation    -   BHA RPM limiter    -   Lower sand screen completions    -   Horizontal liners (cemented or non-cemented)    -   Slotted or pre-perforated liners    -   Gravel pack installations    -   TCP gun deployment    -   Fishing    -   Included in BHA for Firing jars    -   Deploying deep set packers    -   Multi-lateral completions    -   Casing exits

It is an aim of the present invention to obviate or mitigate one or moreof the disadvantages associated with existing downhole tools.

Accordingly, the present invention provides a downhole tool assembly,comprising:

-   -   a first body and a second body arranged to rotate one relative        to the other about a rotation axis and    -   a drive arrangement between the first and the second body for        rotating the first and the second body relative to each other,        wherein the drive arrangement comprises a harmonic drive        comprising a wave generator, a flexible gear and an outer gear,        wherein one of the wave generator, flexible gear and outer gear        is adapted to function as a rotary input component and another        of the wave generator, flexible gear and outer gear is adapted        to function as a rotary output component; and wherein the        downhole tool assembly comprises one or more motors for rotating        a component of the downhole tool assembly, wherein the harmonic        drive is arranged in a couplable relationship with the motor so        that rotation of the motor results in rotation of the first and        the second bodies relative to each other.

Preferably, the remaining one of the wave generator, flexible gear andouter gear is adapted to function as a stationary component of theharmonic drive.

The downhole tool arrangement preferably includes a Bottom Hole Assembly(BHA) wherein at least one of the first and second bodies is included inthe BHA. The downhole tool assembly preferably forms part of adrill-string or work-string.

A harmonic drive is a special type of drive and typically comprises awave generator (typically an elliptical hub or cam sometimes alsoreferred to as an oval bearing), an intermediate gear, aka a flexiblegear, and an outer gear, commonly referred to as a circular gear.Typically, in a harmonic drive, when the outer gear is fixed, the wavegenerator and the flexible gear rotate in opposite directions; when theflexible gear is fixed, the outer gear and the wave generator rotate inthe same direction; and when the wave generator is fixed, the outer gearand the flexible gear rotate in the same direction. Arrangements arepossible where all the three components of the harmonic drive rotate sothat the harmonic drive functions as a differential. Due to its uniqueprinciple of construction, a harmonic drive provides very high or verylow, depending on what is used as an input, transmission ratios (typicalratios include 100:1, 200:1, 300:1 or vice versa etc.) along with hightorque transmission (due to a plurality of teeth meshing at the sametime), torque multiplication (or reduction depending on what is used asan input), very compact construction, rotation precision, low vibrationand absence of backlash. Since harmonic drives are known, it is notnecessary to describe its construction and operation in detail.

Preferably, the first and the second bodies have a common axis ofrotation.

The motor preferably comprises a rotor component for driving thecomponent of the downhole tool assembly and a stator component whereinthe rotary input component of the harmonic drive is arranged in acouplable relationship with the motor so as to transmit rotation fromthe motor via the harmonic drive to the rotary output component of theharmonic drive.

In one arrangement, the rotary input component of the harmonic drive isarranged in a couplable relationship with the rotor component of themotor so as to transmit rotation of the rotor component of the motor viathe harmonic drive to the rotary output component of the harmonic drive.

In another arrangement, the rotary input component of the harmonic driveis arranged in a couplable relationship with the stator component of themotor so as to permit the stator component of the motor to rotate underthe influence of reactive torque acting on the stator component duringrotation of the rotor component of the motor.

In one arrangement, a pair of harmonic drives is provided, wherein in afirst harmonic drive the rotary input component is arranged in acouplable relationship with the rotor component of the motor so as totransmit rotation of the rotor component of the motor via the harmonicdrive to the rotary output component of the harmonic drive, and whereinthe rotary input component of the second harmonic drive is arranged in acouplable relationship with the stator component of the motor so as topermit the stator component of the motor to rotate under the influenceof reactive torque acting on the stator component during rotation of therotor component of the motor and, preferably, wherein the first harmonicdrive is incorporated into the rotary output component of the secondharmonic drive so that when the rotary output component of the secondharmonic drive is rotated, the first harmonic drive rotates as a unitwith the rotary output component of the second harmonic drive in thedirection opposite to the direction of rotation of the rotary outputcomponent of the first harmonic drive. In this arrangement, rotation ofthe rotary output component of the first harmonic drive in oppositedirections is made possible.

In one arrangement, one of the first and second bodies comprises one ofthe rotor component or the stator component of the motor.

In one arrangement, the motor is a downhole motor for rotating acomponent of the downhole tool, such as for example a drill bit. Thedownhole motor is preferably arranged in a power section of the BHA ofthe downhole tool assembly and wherein the rotor component of the motorcomprises a motor shaft extending substantially coaxially with therotation axis of the first body relative to the second body and thestator component comprises a tubular motor housing wherein the housingencloses the motor shaft. The down hole motor may comprise a mud motor,but it will be appreciated that alternative types of downhole motor canbe utilised, e.g. a turbine motor. The motor shaft is preferablyconnected to an end component, which can be a drill bit or some othertool.

In another case, the motor comprises a topmotor at surface wherein therotor component of the motor comprises a drill pipe extending betweenthe BHA and the topmotor. Preferably, the harmonic drive is coupled tothe drill pipe at the rotary input component and to the second body atthe rotary output component. Where drill pipe is used, the downhole toolassembly preferably comprises a second motor in the form of a downholemotor.

The present invention is usable with either drill pipe or coiled tubing.Thus, in one arrangement, the first body comprises a drill piperotatable by a topmotor. In another arrangement, the first bodycomprises non-rotatable coiled tubing. In either of the abovearrangements, i.e. where the first body comprises a drill pipe or coiledtubing, the second body preferably comprises a rotatable component of aBHA.

Thus, in one arrangement, the harmonic drive can be connected betweenthe motor shaft of downhole motor and the rotatable component of theBHA, e.g. a bent portion or a bent sub, so as to utilise the activetorque of the downhole motor to rotate the rotatable component of theBHA with considerable reduction, e.g. in order to orient a bent sub.Rotation in opposite direction can be achieved by coupling the harmonicdrive to the stator component of the downhole motor and coupling thestator component to the rotatable component of the BHA and utilising thereactive torque acting on the stator component to rotate the rotatablecomponent of the BHA.

In another arrangement, the harmonic drive is coupled between a drillpipe and a rotatable component of the BHA, e.g. a bent portion or a bentsub, wherein rotation of the drill pipe is transmitted to the rotatablecomponent of the BHA with considerable reduction, e.g. in order toorient a bent sub or to allow the bent sub to rotate constantly butconsiderably slower than the drill pipe. In the latter case, the drillpipe can thus rotate during directional drilling and thereby slidedrilling can be avoided while the bent portion remains non-rotating orrotates so slowly that the effect of this rotation on the drillingdirection is negligibly small. Furthermore, the harmonic drive of thepresent invention can be equipped with a clutch arrangement, asspecified in more detail below, for selective interruption of the rotaryconnection between the drill pipe and the BHA, e.g. in case of excessivetorque exerted on the BHA by the drill pipe. The clutch arrangement isalso preferably adapted to selectively lock the harmonic drive betweenthe drill pipe and the BHA so that the drill pipe and the BHA rotate asone piece thereby providing for the possibility of drilling straight.The clutch arrangement is also preferably adapted to alter connectionsequence between the motor, the wave generator, the flexible gear, theouter gear and the first or the second body of the BHA so that the firstor the second body can be rotated in opposite directions.

In one arrangement, the harmonic drive is coupled between the motor andthe first or the second body of the BHA, so that the first or the secondbody of the BHA is coupled with either the flexible gear or the outergear so that the first or the second body can be rotated in the desireddirection, or a clutch means is provided enabling first or the secondbody to be selectively coupled with either the outer gear or theflexible gear, so that the first or the second body can be rotated inopposite directions.

In one arrangement, the outer gear is provided in the form of astabiliser mounted around an outer circumference of the downhole toolassembly. In one arrangement, the stabiliser is a non-rotatingstabiliser.

In one arrangement, the outer gear is adapted to function as astationary component in the harmonic drive. Preferably, the outer gearis configured so that it remains stationary in a borehole due tofriction between the outer gear and a wall of the borehole while one ofthe flexible gear or, preferably, the wave generator functions as therotary input component. However, the friction can be overcome when theouter gear is coupled to the motor to be rotated by the motor and theharmonic drive is locked to rotate as a unit together with the motor. Inone arrangement, the outer gear can be provided with a device, e. g. aflywheel, which prevents rotation of the outer gear in the directionopposite to the rotation of the outer gear when it is coupled to themotor and the harmonic drive is locked to rotate as a unit together withthe motor, when the outer gear is required to remain stationary during,the operation of the harmonic drive, and permits rotation of the outergear when the outer gear is coupled to the motor and the harmonic driveis locked to rotate as a unit together with the motor. For example, thedirection opposite to the rotation of the outer gear when it is coupledto the motor and the harmonic drive is locked to rotate as a unittogether with the motor, when the outer gear is required to remainstationary during the operation of the harmonic drive is a direction ofreactive torque acting on the outer gear from a stator component of themotor, when the rotary input component of the harmonic drive is arrangedin a couplable relationship with the stator component of the motor so asto permit the stator component of the motor to rotate under theinfluence of reactive torque acting on the stator component duringrotation of the rotor component of the motor.

In one embodiment, the BHA is an orienting sub in which the relativerotation between the first body and the second body results in thechange of orientation of one of the two bodies with regard to the other.This change in the orientation can be angular, i.e. a change in therotational angle between the first and second bodies due to relativerotation of the first and second bodies about a common axis orlongitudinal, i.e. involving a change in the angle between longitudinalaxes of the first and the second bodies.

In a preferred arrangement, the BHA comprises a bent sub or a bentportion wherein the second body of the downhole tool assembly comprisesthe bent portion. The bent portion has an axis positioned at an angle toa central axis of the downhole tool assembly, wherein rotation of thebent portion around the central axis of the downhole tool assemblyresults in a change of circumferential orientation of the bent sub, andthus in the eventual direction of advancement of the downhole tool. Thebent portion is preferably provided in the form of a bent housingrotatable about the central axis of the downhole tool assembly.

The bent portion or the bent sub may be arranged so that the bend anglein relation to the central axis of the downhole tool assembly can beadjusted downhole. This is achieved, preferably, by providing a bentportion comprising first and second bend members, wherein the first bendmember is co-axial with the central axis of the downhole tool assembly,and the second bend member is rotatably coupled to the first bend memberand rotatable relative thereto about a second axis of rotation which isat a non-zero angle relative to the central axis whereby the relativerotation of the first and second bend members results in the change inthe bend angle between the bent portion and the central axis and whereinthe first and second bend members are arranged to rotate relative toeach other by a harmonic drive according the aspects described above.

Preferably, the harmonic drive comprises at least one clutch arranged soas to selectively vary the transmission of rotation between the harmonicdrive and the motor, so as for example to disable the transmission orenable transmission of rotation with or without reduction and/or so asto change the direction of rotation at the output.

The clutch may be selected from many suitable types, including conicalclutches, freewheels, viscous coupling, Hele-Shaw clutches, fluid drive,wet multi-plate clutch, epicyclical planetary gear system, wet clutch,magnetic inductance and other suitable.

Preferably, actuating means is provided for actuating the clutch, whichcan be provided in any suitable form, including a motor actuator, suchas, for example, an electric actuator, pressure differential actuator(e.g. a spring), weight-on-bit (WOB) actuation, flow rate or flow pulseoperated actuator.

A clutch may be adapted to selectively alternately cooperate with one ormore of the wave generator, the flexible gear and the outer gear so asto enable or restrict rotation of that gear and so as to permit orrestrict rotation of another gear, thereby enabling the change in thedirection of rotation to occur between the first and the second body.The clutch can be active or passive, i.e. adapted to beactivated/deactivated conditionally, e.g. when a certain condition ismet. For example, a passive clutch can be provided between the harmonicdrive and the BHA, the clutch being operable so that when torque exertedon the BHA from the drill pipe exceeds predetermined value, the clutchis activated and the rotary connection between the drill pipe and theBHA is interrupted so that the drill pipe can continue to rotate withoutexerting torque on the BHA.

Each of the first and second bodies preferably comprises a longitudinalaxis. In a preferred embodiment, the longitudinal axes are collinear.Also, in a preferred embodiment, the longitudinal axes coincide with themutual rotational axis of the bodies.

In a further advantageous variation, the harmonic drive may include oneor more additional sets of an wave generator, a flexible gear and anouter gear, wherein the additional set of gears is linked to theexisting set of gears so that the transmission ratio of the harmonicdrive is a product of the transmission ratios of the existing and theadditional sets. The provision of an additional gear set enables thetransmission ratio of the harmonic drive to be set within a wide rangeof ratios, wherein each such ratio provides for a high level ofprecision in moving the first body in relation to the second body. Forexample, by providing a high reduction ratio between (such as the orderof 1/100 or 1/10000 and so on) it is possible to rotate a rotatablecomponent of a BHA very slowly, sufficiently slow so that the relativepositions of the first and second bodies can be adjusted with high levelof accuracy, or to make the rotation so slow that it can be regarded asnon existent, where it is necessary to restrict the rotation of one ofthe two bodies while allowing the other body to rotate. In such anarrangement however, output torque is considerably higher than in asingle-step harmonic drive and it is thus preferred to provide a torquelimiting device at the output of the harmonic drive in order to preventcomponents of the downhole assembly from becoming damaged due toexcessive torque.

In one arrangement, where a drill pipe is used in combination with adownhole motor and a bent sub, the harmonic drive is located above thedownhole motor, but within the BHA and is connected between the drillpipe and a bent portion of the BHA so as selectively to permit therotation of the drill pipe from surface above the harmonic drive whileminimising or preventing altogether rotation of the bent portion. Thisis achieved by carefully selecting the reduction ratio of the harmonicdrive such that the resulting rotation of the bent sub is negligiblyslow compared with the rotation of the drill pipe that it can beregarded as non-existent. Such an arrangement enables directionaldrilling in the preset direction (i.e. when orientation of the bent subis fixed and the bent portion slides as the bit is being rotated) withthe drilling action powered by the downhole motor within the BHA and atthe same time permits the drill pipe to be rotated by the topmotor abovethe bent portion. This arrangement eliminates the need to stop surfacerotation of the drill pipe during directional drilling therebyminimising considerably friction problems in directional drilling.

The provision of a harmonic drive for rotating components of a downholetool eliminates the need for a separate actuator motor. Instead, theharmonic drive uses the power of the primary motor (i.e. a topmotor or adownhole motor) of the downhole tool thereby reducing power consumption.A further effect of this arrangement is that it is not necessary to stopdrilling or other downhole activity in order to adjust the toolorientation as the adjustment can now be done simultaneously with thedrilling or the other activity while the primary motor is in operation.The considerable reduction ratio provided by the harmonic drive providesfor a high precision in the adjustment of the orientation of the tooland requires low torque for functioning or the possibility to slow downthe rotation of a bent portion of a bent sub to a negligible levelduring directional drilling so that the drill pipe upstring the bent subcan rotate at the same speed as the topmotor whereas the bent portionslides thereby setting the required drilling direction for the BHA.Furthermore, a harmonic drive has an inherently compact configurationand fits coaxially around a main longitudinal axis of the tool, thusmaking it easier to manufacture and assemble the tool compared to a toolwith a separate actuator motor which is typically offset from thelongitudinal axis of the drilling tool and thus requires asymmetriclinkage components to be used to connect a drive shaft of the actuatormotor with the rotating components of the sub.

In one arrangement, the rotatable component of the motor comprises aneccentric drive shaft of a downhole motor and the rotary input componentof the harmonic drive is coupled directly to the eccentric drive shaft.The advantage of this arrangement over coupling to the motor shaft ofthe downhole motor is that this reduces the overall length of the tool.

According to a second aspect of the present invention there is provideda directional drilling tool, comprising:

-   -   a first end attachable to a drillstring, and a second end        attachable to a drill bit;    -   a power section located intermediate the first and second ends,        and adapted to provide power to the drill bit;    -   a swivel section having first and second swivel members        non-rotatably attached to the first end and power section        respectively, wherein the second swivel member is rotatably        coupled to the first swivel member and rotatable relative        thereto about a first axis of rotation which is co-axial with a        longitudinal axis of the tool;        a first harmonic drive adapted to selectively rotate the second        swivel member about the first axis of rotation;    -   an adjustable bend section having first and second bend members        non-rotatably attached to the power section and the second end        respectively, wherein the first bend member is co-axial with the        longitudinal axis, and the second bend member is rotatably        coupled to the first bend member and having a second axis        positionable at a non-zero angle relative to the longitudinal        axis;        and a second harmonic drive adapted to selectively rotate the        first and second bend members relative each other so as to vary        the angle between the longitudinal axis and the second axis.

The drilling tool may further comprise a remote control system having anoperator control interface which may include a graphical display meansindicating the path of the tool.

Further preferably, the drilling tool comprises a measuring device, forexample a measurement while drilling (MWD) tool installed, preferably,below the swivel section and, ideally, above the power section. The MWDtool serves to read and measure drilling parameters. The BHA may alsocomprise a logging-while-drilling (LWD) tool in place of or in additionto MWD.

Embodiments of the second aspect of the present invention may compriseone or more features of the first aspect of the present invention andvice versa.

According to a third aspect of the invention there is provided adirectional drilling system, comprising:

-   -   a directional drilling tool according to the second aspect of        the invention;    -   a drill bit attached to the second end of the tool;    -   a measuring device adapted to monitor the orientation and        position of the drill bit;    -   a remote control system having an operator control interface        adapted to receive manual tool control inputs; and    -   an electronic controller adapted to selectively activate the        first and/or second harmonic drives of the tool in response to        signals from the measuring device and/or remote control system.

Each of the swivel and adjustable bend sections may further comprise oneor more positional sensors adapted to communicate the rotationalposition of the swivel and adjustable bend sections to the controller.

Embodiments of the third aspect of the present invention may compriseone or more features of the first or second aspect of the presentinvention and vice versa.

According to a fourth aspect of the invention, there is provided adownhole tool assembly, comprising:

-   -   a first body and a second body arranged to rotate one relative        to the other about a rotation axis and    -   a drive arrangement between the first and the second body for        rotating the first and the second body relative to each other,        wherein the drive arrangement comprises a planetary gearbox        comprising a sun, a planet carrier and an annulus, wherein one        of the sun, planet carrier and annulus is adapted to function as        a rotary input component and another of the sun, planet carrier        and annulus is adapted to function as a rotary output component;        and wherein the downhole tool assembly comprises a motor for        rotating a component of the downhole tool assembly, wherein the        planetary gearbox is arranged in a couplable relationship with        the motor so that rotation of the motor results in rotation of        the first and the second bodies relative to each other.

Embodiments of the fourth aspect of the present invention may compriseone or more features of the first, second and third aspects of thepresent invention.

According to a fifth aspect of the present invention there is provided adirectional drilling tool, comprising:

-   -   a first end attachable to a drillstring, and a second end        attachable to a drill bit;    -   a power section located intermediate the first and second ends,        and adapted to provide power to the drill bit;    -   a swivel section having first and second swivel members        non-rotatably attached to the first end and power section        respectively, wherein the second swivel member is rotatably        coupled to the first swivel member and rotatable relative        thereto about a first axis of rotation which is co-axial with a        longitudinal axis of the tool;    -   a first planetary box adapted to selectively rotate the second        swivel member about the first axis of rotation;    -   an adjustable bend section having first and second bend members        non-rotatably attached to the power section and the second end        respectively, wherein the first bend member is co-axial with the        longitudinal axis, and the second bend member is rotatably        coupled to the first bend member and having a second axis which        is at a non-zero angle relative to the longitudinal axis; and    -   a second planetary box adapted to selectively rotate the first        and second bend members relative each other so as to vary the        angle between the longitudinal axis and the second axis.

Embodiments of the fifth aspect of the present invention may compriseone or more features of the first, second, third and fourth aspects ofthe present invention.

According to a sixth aspect of the invention there is provided adirectional drilling system, comprising:

-   -   a directional drilling tool according to the fifth aspect of the        invention;    -   a drill bit attached to the second end of the tool;    -   a measuring device adapted to monitor the orientation and        position of the drill bit;    -   a remote control system having an operator control interface        adapted to receive manual tool control inputs; and    -   an electronic controller adapted to selectively activate the        first and/or second planetary gearboxes of the tool in response        to signals from the measuring device and/or remote control        system.

Embodiments of the sixth aspect of the present invention may compriseone or more features of the first, second, third, fourth and fifthaspects of the present invention.

One of the advantages of the use of a planetary gear box is that aplanetary gearbox has a considerable durability in high shockenvironments compared to other transmission devices, especially incoaxial transmission.

The present invention is particularly useful in a directional drillingsub having a bent portion where it is necessary to be able to rotate thebent portion with respect to the central axis of the drillstring inorder to change the rotational orientation of the bent portion andthereby to change the direction of drilling.

It will be however will be appreciated that the present invention is notlimited to the use in a bent sub only and indeed is useful in otherapplications where it is necessary control relative rotation of at leasta pair of components in a downhole tool assembly. Coupling the harmonicdrive to a primary motor of a downhole tool assembly, e.g. a topmotor ora downhole motor causes the harmonic drive to use the rotation of theprimary motor to induce relative rotation of various parts of a downhole tool assembly which need to be controlled in a desired manner andwhich cannot be directly rotated by the primary motor. At the same time,and equally importantly, the incorporation of the harmonic drive into adownhole tool assembly of the present invention does not result in theloss of important primary functions of the downhole tool, e.g. theability to drill or advance straight in the well bore.

For example, in drill pipe drilling, the present invention, in one modeof operation, provides for the rotation of the drill pipe duringdirectional drilling while the bent housing is practically not rotating,thereby mitigating the friction problems associated with slide drillingand increasing the rate of penetration during directional drillingcompared to the conventional slide drilling. Whereas in another mode ofoperation, the present invention provides for the rotation of thedrillstring and the bent housing as one piece, thereby keeping theability of the downhole tool assembly to drill straight ahead as opposedto drilling alternately in opposite directions when a generally straightpath is required. Furthermore, the present invention allows the rotationof the drill pipe rotated by the topmotor to be used to orient thetoolface and/or adjust the bend angle. Also, in drill pipe drilling, theharmonic drive in combination with an active clutch provide for therotation of the drill pipe together with a BHA as one piece therebypermitting straight drilling. Also in drill pipe drilling, the harmonicdrive in combination with a passive clutch provide for overtorque reliefby interrupting the rotary connection between the drill pipe and the BHAso that the drill pipe can rotate without imparting torque on the BHA.

In both coiled tubing drilling and drill pipe drilling, the presentinvention allows the rotation of the downhole motor to be used to orientthe toolface and/or to adjust the bend angle.

In both coiled tubing drilling and drill pipe drilling, the presentinvention allows the reactive torque acting on the stator component ofthe downhole motor to be utilised to orient the rotatable component ofthe BHA, such as the bent portion, as well as to correct the toolfacewhich tends to be displaced due to the reactive torque duringdirectional drilling. The use of both the active and reactive torques ofa downhole motor permits the rotation of the rotatable component inopposite directions.

Thus, advantages of the present invention include the ability for theupper string to be rotated independently of any down-hole apparatus thatis run below without imparting any torque or rotation to the apparatusbeing deployed and/or allowing the upper string to be rotated fasterthan the apparatus being deployed with a reduction in torque transmittedfrom the work-string to the said apparatus.

Further still, it may allow a predetermined torque to be held on thedownhole tool without rotation of said downhole tool being deployed bymaintaining a predetermined rotational speed in the work string above.

Further still, it may allow a predetermined torque limit to be set toavoid excess torque being transmitted into downhole tool and/or it mayallow multiple tools to be run and functioned independently in the samework string so as to allow a combination of variable speed and torque tobe conveyed to many parts of the same work string.

Moreover, it may allow multiple tools to be run and functionedindependently in the same work string so as to allow a combination ofvariable speed and torque and tool lock out to be conveyed to many partsof the same work string and/or it may allow tools to be locked toprovide full one to one drive from work string to the downhole tool thatis being deployed.

Further still, it may allow the upper string to be rotated slower thanthe apparatus being deployed with a considerable reduction in torquetransmitted from the work-string to the said apparatus and/or it mayallow the upper string to be rotated faster than the apparatus beingdeployed with an increase in torque transmitted from the work-string tothe said apparatus.

The present invention may find application in several applications,including:

-   -   Wellbore cleaning while drilling    -   Slide drilling    -   Enhanced RSS    -   Stick slip mitigation    -   BHA RPM limiter    -   Torque reduction    -   Lower sand screen completions    -   Horizontal liners (cemented or non-cemented)    -   Slotted or pre-perforated liners    -   Gravel pack installations    -   TCP gun deployment    -   Fishing    -   Included in BHA for Firing jars    -   Deploying deep set packers    -   Multi-lateral completions    -   Casing exits

Embodiments of the present invention will now be described by way ofexample only, with reference to the accompanying drawings in which:

FIGS. 1 to 3 and 5 to 8 a and 9 to 11 are schematic illustrations oflongitudinal cross-sectional partial views of respective first, second,third, fourth, fifth, sixth, seventh, eighth, ninth and tenthembodiments of a downhole tool of the invention;

FIG. 4 is a schematic illustration of a longitudinal cross-sectionalview of the embodiment of FIG. 3;

FIG. 8 b is a transverse cross-section of an outer gear having a devicepermitting rotation of the outer gear in one direction and preventingrotation in the opposite direction;

FIGS. 12 and 13 are schematic partially cross-sectional side views ofvariations of a downhole assembly of the invention having a bent sectionfor directional drilling; and

FIG. 14 is a further variation of a downhole assembly of the inventionhaving an adjustable bend section and a swivel section;

FIGS. 15 and 16 are cross-sectional partial side views showing anadjustable bend section in more detail.

In the presently described embodiments the downhole tool assembly of theinvention is described in the form of a directional drilling tool, aswill be described in more detail below, comprising a BHA having a bentportion having a bent axis wherein the orientation of the bent axis inrelation to a central axis of the BHA can be adjusted downhole. It willbe appreciated that embodiments of the invention as described below,suitably adapted as would be readily apparent to a person skilled in theart, can be used in other downhole tools, such as for example logging,fishing, completions etc, where it is required to rotate a first bodyrelative to a second body about a rotation axis.

Initially, referring to FIGS. 1 to 8 a and 9 to 11, the generalprinciples of the invention will be described. For brevity, somefeatures common for some or all the Figures have been denoted usingcommon reference numerals.

A downhole tool assembly 1, 2, 3, 4, 5, 5 a, 6, 7, 8, 9, 5000 accordingto a first aspect of the present invention comprises a BHA 10, 20, 30,40, 50, 50 a, 60, 70, 80, 90, 5050 comprising a bent portion (notshown). The downhole tool assembly 1, 2, 3, 4, 5, 5 a, 6, 7, 8, 9, 5000comprises a first body 11, 21, 31, 41, 51, 51 a, 61, 71, 81, 91, 5051and a second body 12, 22, 32, 42, 52, 52 a, 62, 72, 82, 92, 5052arranged to rotate one relative to the other about a rotation axis 1000which is also a common axis of the first and second bodies. In thepresently described embodiments, the downhole tool assembly 1, 2, 3, 4,5, 5 a, 6, 7, 8, 9, 5000 forms part of a drill string, but it will beappreciated that the present invention can be incorporated into otherworkstrings. At least one of the first or second bodies belongs to theBHA 10, 20, 30, 40, 50, 50 a, 60, 70, 80, 90, 5050.

In the presently described embodiments, in the BHA 10, 20, 30, 40, 50,50 a, 60, 70, 80, 90, 5050 rotation of the first body 11, 21, 31, 41,51, 51 a, 61, 71, 81, 91, 5051 relative to the second body 12, 22, 32,42, 52, 52 a, 62, 72, 82, 92, 5052 results in the change of orientationof one of the two bodies with regard to the other. The change in theorientation can be angular, i.e. involve a change in the relativerotational disposition of the first and second bodies or longitudinal,i.e. involving a change in the angle between longitudinal axes of thefirst and second bodies or both.

The downhole tool assembly 1, 2, 3, 4, 5, 5 a, 6, 7, 8, 9, 5000comprises a drive arrangement 1001 for rotating the first and the secondbodies relative to each other. The drive arrangement comprises aharmonic drive 13, 23, 33, 43, 53, 53 a, 63, 73, 83, 93, 5053 comprisinga wave generator 14, 24, 34, 44, 54, 54 a, 64, 64′, 74, 84, 94, 5054 aflexible gear 15, 25, 35, 45, 55, 55 a, 65, 65′, 75, 85, 95, 5055 and anouter gear 16, 26, 36, 46, 56, 56 a, 66, 66′, 76, 86, 96, 5056. As willbecome more apparent from the following description, one of the wavegenerator, flexible gear and outer gear is adapted to function as arotary input component and another of the wave generator, flexible gearand outer gear is adapted to function as a rotary output component.

Still referring to FIGS. 1 to 8 a and 9 to 11, the downhole toolcomprises a motor (not shown) for rotating a component of the downholetool assembly 1, 2, 3, 4, 5, 5 a, 6, 7, 8, 9, 5000. The harmonic drive13, 23, 33, 43, 53, 53 a, 63, 73, 83, 93, 5053 is arranged in acouplable relationship with the motor so that rotation of the motorresults in rotation of the first and the second bodies relative to eachother.

The motor comprises a rotor component 17, 47, 57, 57 a, 67, 77, 87, 97,5057 (FIGS. 1, 5 to 8 a and 9 to 11), for driving a component thedown-hole assembly, e.g. a drill bit and a stator component 28, 38(FIGS. 2 to 4). In the embodiments of FIGS. 2 to 4, the stator component28, 38 is a housing of a downhole motor, as will be discussed below. Therotary input component of the harmonic drive 13, 23, 33, 43, 53, 53 a,63, 73, 83, 93, 5053 is arranged in a couplable relationship with themotor so as to transmit rotation from the motor via the harmonic drive13, 23, 33, 43, 53, 53 a, 63, 73, 83, 93, 5053 to the rotary outputcomponent of the harmonic drive 13, 23, 33, 43, 53, 53 a, 63, 73, 83,93, 5053.

In the embodiments shown in FIGS. 1, 5 to 8 a and 9 to 11, the rotaryinput component of the harmonic drive 13, 43, 53, 53 a, 63, 73, 83, 93,5053 is arranged in a couplable relationship with the rotor component17, 47, 57, 57 a, 67, 77, 87, 97, 5057 of the motor so as to transmitrotation of the rotor component 17, 47, 57, 57 a, 67, 77, 87, 97, 5057via the harmonic drive 13, 43, 53, 53 a, 63, 73, 83, 93, 5053 to therotary output component of the harmonic drive 13, 43, 53, 53 a, 63, 73,83, 93, 5053. In FIGS. 1, 5 to 8 a and 9 to 11, the rotary inputcomponent is the wave generator 14, 44, 54, 54 a, 64, 64′, 74, 84, 94,5054 and the rotary output component is the flexible gear 15, 45, 55, 55a, 65′, 75, 85, 95, 5055. Additionally, in FIGS. 9 and 10, the outergears 86, 96 can function as the rotary output components as will bespecified below.

In the embodiments shown in FIGS. 2 to 4, the rotary input component ofthe harmonic drive 23, 33 is arranged in a couplable relationship withthe stator component (housing) 28, 38 of the motor so as to permit, whenrequired, the stator component 28, 38 of the motor to rotate under theinfluence of a reactive torque acting on the stator component 28, 38during rotation of the rotor component of the motor. In FIGS. 2 to 4,the rotary input component, in this case the flexible gear 25, 35 of theharmonic drive 23, 33 is coupled to the stator component (housing) 28,38 to enable transmission of rotation via the harmonic drive 23, 33using the reactive torque of the stator component (housing) 28, 38. Inthis embodiment, although the rotary output component is the wavegenerator 24, 34, the rotation at the output is idle, i.e. the wavegenerator rotates without transmitting the rotation anywhere, whereasthe reactive rotation of the stator component (housing) 28, 38 achievedby the provision of the harmonic drive 23, 33 is the actual usefuloutput. The outer gear 26, 36 functions as a stationary component of theharmonic drive when the harmonic drive is open for transmission.

In FIGS. 1 to 6, the motor is a downhole motor, e.g. a mud motor, forrotating a component of the downhole tool assembly, such as for examplea drill bit. The downhole motor is normally arranged in a power sectionof the down hole tool assembly and the rotor component of the motorcomprises a motor shaft 17, 87, 97 shown extending substantiallycoaxially with the rotation axis 1000. The embodiments of FIGS. 2, 3 and4 also include motor shaft which is not visible in the drawings becausethe harmonic drive 23, 33 is positioned above the power section in theseembodiments.

In the embodiments of FIGS. 1 to 6, the downhole motor comprises atubular housing 18, 28, 38, 88, 98, which encloses the motor shaft andconstitutes a reactive component of the motor. The BHA of FIGS. 1 to 6is coupled to non-rotatable coiled tubing upstring (left-hand side ofthe drawings).

Thus, in FIGS. 1, 5 and 6, the harmonic drive 13, 83, 93 is connectedbetween the motor shaft 17, 87, 97 of downhole motor and the rotatablecomponent 12, 82, 92 of the BHA, e.g. a bent portion or a bent sub, soas to utilise the active torque of the downhole motor to rotate therotatable component 12, 82, 92 of the BHA, e.g. to orient the bent sub.Rotation in the opposite direction can be achieved by coupling aharmonic drive 22, 32 to the stator component (housing) 28, 38 of thedownhole motor and utilising the reactive torque of the stator componentas illustrated in FIGS. 2 to 4. Thus, although not shown in FIGS. 1, 5and 6, a pair of harmonic drives can be included in a BHA, one coupledto motor shaft 17 as shown in FIGS. 1, 5 and 6 and the other coupled tomotor housing 18 above the power section as shown in FIGS. 2 to 4. InFIGS. 1, 5 and 6, the outer gear 16, 86, 96 normally functions as astationary component of the harmonic drive 13, 83, 93 when the harmonicdrive is open for transmission, except FIG. 5, where the outer gear 86,can operate as a rotary output component in a specific mode of operationof the harmonic drive 83, as will be described below.

In FIGS. 7 to 8 a, and 9 to 11, the motor is a topmotor at surface andthe rotor component of the motor comprises a drill pipe extendingbetween the BHA and the topmotor. In FIGS. 7 to 8 a, and 9 to 11,housing 48, 58, 58 a, 68, 78, 5058 of the BHA is coupled to a drill pipeso as to be rotated by the drill pipe which functions as a rotorcomponent 47, 57, 57 a, 67, 77, 5057. Additionally (although not shownin the drawings), the downhole tool assembly of FIGS. 7 to 8 a, and 9 to11 preferably comprises downhole motor as a second additional motor,e.g. for drilling straight ahead.

In FIGS. 7 to 8 a, and 9 to 11, the harmonic drive 43, 53, 53 a, 63, 73,5053 is coupled between the drill pipe and the rotatable component 42,52, 52 a, 62, 72, 5052 of the BHA, so that rotation of the drill pipe istransmitted to the rotatable component 42, 52, 52 a, 62, 72, 5052 of theBHA, e.g. to orient the bent sub or make it rotate considerably slowerthan the drill pipe. The latter possibility allows the drill pipe torotate during directional drilling while the bent portion remainsnon-rotating or rotates so slowly that the effect of this rotation onthe drilling direction is negligibly small. Thus, slide drilling andfriction problems associated with it can be avoided. In FIGS. 7 to 8 a,and 9 to 11, the outer gear 46, 56, 56 a, 66, 76, 5056 is normallynon-rotatable in the borehole due to friction with the borehole wallsand thus normally serves as the stationary component of the harmonicdrive, 45, 55, 55 a, 65, 75, 5055 with some exceptions as will bedescribed below.

FIGS. 12 and 13 illustrate examples of downhole assemblies in which thepresent invention can be incorporated. In FIGS. 12 and 13, the downholeassemblies comprise drilling BHAs 1210, 1310, respectively. BHA 1210,1310 comprises a bent portion 1211, 1311 and the bent portion 1211, 1311comprises the second body of the down hole tool assembly of the presentinvention. The bent portion 1211, 1311 has an axis positioned at anangle to the central axis 1000 of the downhole tool assembly. Rotationof the bent portion 1211, 1311 around the central axis 1000 of thedownhole tool assembly results in a change of rotational orientation ofthe bent portion 1211, 1311 in relation to the rest of the drill stringand thus in the eventual direction of drilling. The bent portion 1211,1311 can also be configured so that its bend angle in relation to thecentral axis 1000 of the downhole tool assembly can be adjusted downholeas will be described below.

FIG. 12 illustrates a BHA 1210 having a harmonic drive 1213 arranged inthe BHA 1210 similar to the arrangements of FIGS. 1, 5 and 6, i.e. theharmonic drive 1213 is connected between a motor shaft 1217 of adownhole motor 1260 and the bent portion 1211 so as to utilise theactive torque of the downhole motor shaft 1217 to rotate the bent sub1211 and thus to change drilling direction. In the BHA 1210, the motorshaft 1217 is coupled to a wave generator 1214, which drives a flexiblegear 1215 in order to rotate the bent portion 1211 while an outer gear1216 coupled to motor housing 1218, which in turn is coupled tonon-rotatable coiled tubing sting 1240, remains stationary.

FIG. 13 illustrates a BHA 1310 having a harmonic drive 1313 arranged inthe BHA 1310 similar to the arrangements of FIGS. 7 to 8 a and 9 to 11,i.e. the harmonic drive 1313 is coupled between a drill pipe 1340rotatable from surface and the bent portion 1311, but above a downholemotor 1360, so that rotation of the drill pipe 1340 is transmitted tothe entire BHA 1310 and the BHA 1310 is thus rotated as a unit with thedownhole motor 1360 in order to orient the bent portion 1311 or make itrotate considerably slower than the drill pipe during directionaldrilling. The latter possibility allows the drill pipe 1340 to rotateduring directional drilling while the bent portion 1311 remainsnon-rotating or rotates so slowly that the effect of this rotation onthe drilling direction is negligibly small. Thus, slide drilling andfriction problems associated with it can be avoided. In the BHA 1310, anouter gear 1316 of the harmonic drive 1313 is normally non-rotatable inthe borehole due to friction with the borehole walls and thus normallyserves as the stationary component of the harmonic drive 1313 whereasthe drill pipe 1340 rotates a wave generator 1314, which drives aflexible gear 1315 in order to rotate the BHA 1310 as a whole.

Often, a downhole assembly comprises a measuring device, for example ameasurement while drilling (MWD) tool to read and measure drillingparameters. As shown in FIGS. 12 and 13, an MWD tool 1290, 1390respectively installed above the downhole motor 1260, 1360.

FIG. 14 shows a BHA 1410 having an adjustable bend portion 1411, similarto the bent portions 1211, 1311, but in which the bend angle α of thebent portion 1411 in relation to the central axis 1000 of the BHA 1410can be adjusted. This is achieved by providing the bent portion 1411with first and second bend members 1430, 1431, wherein the first bendmember 1431 is co-axial with the central axis 1000 of the BHA 1410 andis non-rotatably attached to housing 1418 of downhole motor 1460 belowthe motor 1460, and the second bend member 1431 is rotatably coupled tothe first bend member 1430 and has a second axis 1010. The angle αbetween the second axis and the central axis 1000 can be changed betweenzero and α_(m) degrees. A joint is provided between the first and secondbend members 1430, 1431 such that the relative rotation of the first andsecond bend members 1430, 1431 via the joint results in the change inthe value of bend angle α between the axis 1010 of bent portion 1411 andthe central axis 1000. A harmonic drive 1413 is provided between thefirst and second bend members 1430, 1431 to rotate the first and secondbend members 1430, 1431 relative to each other in the same manner asdescribed above in relation to FIG. 12. In the embodiment of FIG. 14, inorder to adjust the rotational orientation of the bent portion 1411 aswivel section 1480 is provided having first and second swivel members1432, 1433. The first swivel member 1432 is non-rotatably attached to adrill string 1440 and the second swivel member 1433 is non-rotatablyattached to the housing 1418 of the downhole motor 1460 above the motor1460. The first and second swivel members 1432, 1433 are rotatablycoupled to each other and rotatable relative to each other about an axis1011 of rotation which is co-axial with the central axis 1000. Aharmonic drive 1423 is provided between the first and second bendmembers 1432, 1433 to rotate the first and second swivel members 1432,1433 relative to each other in the same manner as described above inrelation to FIG. 13.

FIGS. 15 and 16 illustrate a joint 1480 between the first and secondbend members 1430, 1431 which allows the angle between the second axis1010 and the central axis 1000 can be varied. The joint 1480 is providedby a spherical spline member 1481 which engages a bend adjustmentcoupling 1482. The spherical spline member 1481 is non-rotatablyconnected with one end of a bend adjustment sleeve 1445. The bendadjustment sleeve 1445 is coupled to a harmonic drive 1413 at the otherend of the bend adjustment sleeve 1445. The bend adjustment coupling1482 is non-rotatably coupled with the second bend member 1431. The bendadjustment coupling 1482 has a longitudinal rotation axis 1020 which isoriented at an angle β=α_(max)/2 to the central axis 1000 and the secondaxis 1010. The bend adjustment coupling 1482 is rotated by a harmonicdrive 1413 in manner similar to that described with reference to FIG.12. Specifically, motor shaft 1417 of a downhole motor (not shown)rotates a wave generator 1414 via a clutch 1419 controlled by actuator1499 in a similar manner as described with reference to FIG. 1. The wavegenerator 1414 drives a flexible gear 1415 in order to rotate the bendadjustment sleeve 1445 together with the spherical spline member 1481,which in turn causes rotation of the bend adjustment coupling 1482 aboutthe rotation axis 1020 through 180 degrees. An outer gear 1416 coupledto the first bend member 1430 which in turn is non-rotatably coupled tomotor housing (not shown) remains stationary. The rotation of the bendadjustment coupling 1482 about the rotation axis 1020 through 180degrees causes the rotation of the second bent member 1431 aboutrotation axis 1020 during which the angle β and a angle between therotation axis 1020 and the second axis 1010 either add up or subtractresulting in the change of the angle α between the second axis 1010 andthe central axis 1000 between zero and α_(max) degrees. In FIG. 15 thesecond bent member 1431 is shown fully bent at an angle α_(max) to thecentral axis 1000, whereas in FIG. 16 the axis 1010 of second bentmember 1431 is aligned at zero degrees with the central axis 1000. Themotor shaft 1417 has universal joints which allow the motor shaft tocomply with the change of the angle between the second axis 1010 and thecentral axis 1000.

The harmonic drive 13, 53, 53 a, 63, 73, 83, 93 comprises a clutch orclutches arranged so as to selectively vary the transmission of rotationbetween the harmonic drive and the motor or to selectively alternatelycooperate with one or more of the wave generator, the flexible gear andthe outer gear so as to enable or restrict rotation of a gear and so asto permit or restrict rotation of another gear, thereby enabling thechange in the direction of rotation between the first and the secondbody, or to selectively interrupt the rotary connection between thedrill pipe and the BHA, e.g. in case of too high torque exerted on theBHA by the drill pipe. The clutch can be a passive clutch, i.e. adaptedto be activated/deactivated conditionally, e.g. when a certain conditionis met, e.g. when torque exerted on the BHA from the drill pipe exceedspredetermined value, the clutch is activated and the rotary connectionbetween the drill pipe and the BHA is disconnected; or an active clutch,i.e. activatable by a positive control signal, such as operator's signalfrom surface.

In FIG. 1, clutch 19 is movably mounted on the shaft 17 to engage ordisengage the wave generator 14 so as to respectively enable or disabletransmission through the harmonic drive 13. Clutch 19 is driven by anactuator 199. Specifically, when the clutch 19 is engaged with the wavegenerator 14, rotation from the motor shaft 17 is transmitted by thewave generator 14 to the flexible gear 15 which rotates the second body12, which can be e.g. a bent sub, in the direction opposite to thedirection of rotation of the motor shaft 17. When the clutch 19 isdisengaged from the wave generator 14, the motor shaft 17 rotates freelywithout transmitting rotation to the wave generator 14. The outer gear16 is non-rotatably mounted on the first body 11, i.e. the motor housing18 which is normally stationary and thus serves as the stationarycomponent in the harmonic drive 13.

In FIG. 2, clutch 29 is movably mounted on the inner side of the firstbody 21 to engage or disengage the wave generator 24. When the clutch 29is disengaged, the housing 28 (together with the flexible gear 25) areable to rotate under the influence of a reactive torque acting on themotor housing 28 from the motor shaft and the rotation is transmitted tothe wave generator 24 which rotates freely, as described above, withouttransmitting the rotation further, the resulting useful output rotationbeing the rotation of the housing 28. The outer gear 26 is non-rotatablymounted on the first body 11, i.e. a portion of non-rotational coiledtubing, and thus serves as the stationary component in the harmonicdrive 23. When the clutch 29 is engaged with the wave generator 24, thewave generator becomes locked to the coiled tubing so that no rotationis possible within the harmonic drive 23. Thus, the coiled tubing, theharmonic drive 23 and the motor housing 22 become a stationary unit.Clutch 29 is driven by an actuator 299.

In FIGS. 3 and 4, when clutch 39 is disengaged, the housing 38 togetherwith the flexible gear 3 are able to rotate under the influence of areactive torque acting on the motor housing 38 from the motor shaft andthe rotation is transmitted to the wave generator 34 which rotatesfreely together with the clutch 39, as described above, withouttransmitting the rotation further, the resulting useful output rotationbeing the rotation of the housing 38. The outer gear 36 is non-rotatablymounted on the first body 31, i.e. a portion of non-rotational coiledtubing, and thus serves as the stationary component in the harmonicdrive 33 When the clutch 39 engages the housing 38 (and the flexiblegear 35), the flexible gear 35 together with the housing 38 becomelocked to the coiled tubing (first body 31) via the clutch 39 so that norotation is possible within the harmonic drive 33. Thus, the coiledtubing, the harmonic drive 33 and the motor housing 32 become astationary unit. This arrangement prevents the reactive torque acting onthe housing 38 from acting on the components of the harmonic drive 33,especially the flexible gear, when the harmonic drive 33 is locked.Instead, the reactive torque acts on the clutch 39. Clutch 39 is drivenby an actuator 399.

In FIG. 5, the wave generator 84 acts as the rotary input component andis rotated by the motor shaft 87. When clutch 89 is moved fully to theright along arrow B, the left portion 85 a of the flexible gear 85engages surface A1 of the first body 81, i.e. the motor housing 88,whereas the right portion of the outer gear 86 engages surface A2 of thesecond body 82, e.g. a bent sub housing, and splines 891 of the outergear 86 disengage. In this position, the outer gear 86 rotates at theoutput in the same direction as the shaft 87 and thus rotates the secondbody 82 whereas the flexible gear 85 is locked to the motor housing 88,which is normally stationary, and thus the flexible gear 85 also remainsstationary. When the clutch 89 is moved fully to the left along arrow B,the right portion 85 b of the flexible gear 85 engages surface B1 of thesecond body 82, whereas the left portion of the outer gear 86 engagessurface B2 of the second body 82 and splines 891 of the outer gear 86disengage. In this position, the flexible gear 85 rotates at the outputin the direction opposite to the direction of rotation of the shaft 87and thus rotates the second body 82 whereas the outer gear 86 is lockedto the motor housing 88 and remains stationary. When the clutch 89 is inan intermediate position, splines 891 lock the outer gear 86 to each ofthe first and second bodies, 81, 82 thereby locking the harmonic drive83 altogether. Actuator 899 is provided for operating the clutch 89.

In FIG. 6, clutch 991 is movable by actuator 999 right or left alongarrow C and clutch 992 is spring actuated and is movable along arrow Dalso by actuator 999. When the clutch 991 is the fully left position,the clutch 991 engages the flexible gear 95 so that the flexible gear 95is locked to the first body 91, i.e. the motor housing 98 which isnormally stationary, and thus the flexible gear 95 also remainsstationary. At the same time, the clutch 992 engages shaft 97 and thewave generator 94 so that the wave generator 94 is rotated by the shaft97. The output rotation is provided by the outer gear 96 which rotatesin the same direction as the shaft 97 and thus rotates the second body92, e.g. a bent sub housing, via a first freewheel 994 which allowsrotation only in one direction, presently clockwise. When the clutch 991is in an intermediate position, the clutch 991 engages the outer gear 96so that the outer gear 96 is locked to the motor housing 98 which isnormally stationary, and thus the outer gear 96 also remains stationary.At the same time, the clutch 992 engages shaft 97 and the wave generator94 so that the wave generator 94 is rotated by the shaft 97. The outputrotation is provided by the flexible gear 95 which rotates in thedirection opposite to the direction of rotation of the shaft 97 and thusrotates the second body 92, e.g. a bent sub housing, via a freewheel 995which allows rotation only in one direction, presently anticlockwise.When the clutch 991 is in the fully right position, the clutch 991 isengaged with the outer gear 96 so that the outer gear 96 is locked tothe motor housing 98 which is normally stationary, and thus the outergear 95 also remains stationary whereas the clutch 992 disengages thewave generator 94 and engages the flexible gear 95 which thus alsobecomes locked to the motor housing 98. In this position, no rotation istransferred from the shaft 97 to the wave generator 94 whereas theharmonic drive 93 is locked and cannot transmit rotation.

Although not illustrated, in the arrangement of FIG. 7, a safety clutchcan be provided between the harmonic drive 43 and the drill-string abovethe BHA. Such a clutch can be sensitive to the torque exerted on the BHAand if the torque exceeds a certain predetermined value, the clutchdisconnects the BHA from the upper string and the overtorque is borne bythe clutch instead of the BHA thereby mitigating any potential damage tothe BHA or other parts of the drill-string. Otherwise, in the embodimentof FIG. 7, rotation by a drill pipe of the BHA housing 48 is transmittedto the wave generator 44 first, then to the flexible gear 45 whichrotates the second body 42, e.g. a bent sub, in the direction oppositeto the direction of rotation of the drill pipe, while the outer gear 46remains non-rotational due to friction with the borehole walls.

In FIGS. 8 and 9, spring action clutches 59, 69 are provided to lock therotating BHA housing 58, 68 to the outer gears 56, 66 causing thenormally stationary, non-rotatable, due to friction with the boreholewalls, outer gears 56, to rotate as a unit with the housing 58, 68 andlocking the harmonic drive 53, 63 so that the second rotating body 52,62 also rotates as a unit with the housing 58, 68 without reduction.Clutches 59, 69 are spring activated via weight-on-bit (WOB) actuation,as indicated by arrows X in FIGS. 8 and 9. When the clutches 59, 69 aredisengaged, rotation by a drill pipe of the BHA housing 58, 68 istransmitted to the wave generator 54, 64 first, then to the flexiblegear 55, 65 which rotates the second body 52, 62, e.g. a bent sub, inthe direction opposite to the direction of rotation of the drill pipe,while the outer gear 56, 66 remains non-rotational due to friction withthe borehole walls.

In the embodiments described with reference to FIGS. 7 and 8 above andFIGS. 9 and 10 below, the outer gear 46, 56, 66, 76 is required to benon-rotating, because it serves both as a stationary component ofharmonic drive 43, 53, 63, 73 and a sliding stabiliser, e.g. indirectional drilling, and is thus designed to have high frictionqualities to engage the borehole walls without rotation. However, theouter gear 46, 56, 66, 76 experiences a reactive torque from a motorshaft rotating downstring of the outer gear 46, 56, 66, 76. Thisreactive torque attempts to rotate the outer gear 46, 56, 66, 76 in theopposite direction, typically anticlockwise. On the other hand, theouter gear 56, 66, 76 of FIGS. 8, 9 and 10 is required to rotate whenthe clutch 59, 69, 79 locks the harmonic drive 53, 63, 73 and thus canexperience excessive friction which can be damaging to the outer gear56, 66, 76. FIGS. 8 a and 8 b depict arrangements addressing this issue.

An embodiment shown in FIG. 8 a is similar to the embodiment of FIG. 8and therefore numerals which indicate the same features as those of FIG.8 have been used in FIG. 8 a with the addition of “a” at each referencenumeral. As shown in FIG. 8 a, flywheels 560 a are provided between theouter gear 56 a and each of the housing 58 a and the second body 52 a,which can be e.g. a bent sub. The flywheels 560 a only allow rotation inone direction (arrow W) which is the same as the direction of rotationof the housing 58 a. Thus, when the clutch 59 a is disengaged, the outergear 56 a remains non-rotational because the flywheels 560 a prevent theouter gear 56 a from rotating in the direction opposite to the oneindicated by arrow W under the influence of a reactive torque. On thecontrary, when the clutch 59 a is engaged, the flywheels 560 a allow theouter gear 56 a to rotate in the same direction as the housing 58 a(arrow Y). In FIG. 8 b an alternative to providing flywheels 560 a ofFIG. 8 a is shown in the form an outer gear 56 b which itself is formedas a flywheel 560 b with engaging members 561 b which engage theborehole wall to prevent rotation in one direction and release whenrotation is attempted in the opposite direction. It is beneficial toinclude flywheels 560 a or 560 b into the embodiments of FIGS. 7, 8, 9and 11.

The embodiment of FIG. 9 is similar to that of FIG. 8. Additionally inFIG. 9, the harmonic drive 63 includes an additional set of componentscomprising a wave generator 64′, a flexible gear 65′ and an outer gear66′ wherein the wave generator 64′ is linked with the flexible gear 65.In this arrangement, the transmission ratio of the harmonic drive 63 isa product of the transmission ratio between wave generator 64 and theflexible gear 65 and the transmission ratio between the wave generator64′ and the flexible gear 65′. The provision of an additional set ofcomponents dramatically increases the reduction ratio of the harmonicdrive 66 and thus provides for a high level of precision in moving thefirst body 61 in relation to the second body 62 or slows down therotation of the second body to a negligible level, so that the firstbody (drill pipe) 61 can rotate while the second body (bent portion) 62remains virtually non-rotating, thereby eliminating friction problemscaused by the sliding of the drill pipe and the bent portion duringconventional slide drilling.

In FIG. 10, the function of the BHA 70 and the function of the clutch 79in the BHA 70 are similar to the function of the BHAs 50 and 60 andclutches 59, 69 of FIG. 8, 9 with the difference that the clutch 79 isarranged to selectively lock the rotating BHA housing 78 to the secondbody 72 (e.g. a bent sub) rather than to the outer gear 76 with the sameeffect of causing the normally stationary outer gear 76, to rotate as aunit with the housing 78 and locking the harmonic drive 73. Furthermore,the clutch 79 is activated by fluid pressure differential created in arestricted area 799. When the clutch 79 is disengaged, the BHA 70functions in the same manner as described above in connection with FIGS.8 and 9.

In FIG. 11, the function of the BHA 5050 and the function of the clutch5059 in the BHA 5050 are similar to the function of the BHAs 50 and 60and clutches 59, 69 of FIG. 8, 9 with the difference that the clutch5059 is arranged to selectively lock the rotating BHA housing 5058 tothe outer gear 5056 without moving the wave generator 5054 axially withrespect to the flexible gear 5055 and thus preventing the wave generator5054 and the flexible gear 5055 from damage. More specifically, in orderto engage the wave generator 5054 to lock the harmonic drive 5053, theclutch 5059 is arranged to slide axially with respect to both the wavegenerator 5054 and the outer gear 5056 by, for example, providing springloaded thrust bearings 5200, 5201, respectively between the clutch 5059and each of the outer gear 5056 and the wave generator 5054. The outergear 5053, the wave generator 5054 and the flexible gear 5055 remainstationary in the axial direction, by providing a suitable stop means,for example thrust bearings 5300, 5400, respectively between the wavegenerator 5054 and the second body 5052 mounting the flexible gear 5055and between the outer gear 5056 and the second body 5052. When theclutch 5059 engages the wave generator 5054, the clutch is allowed toslide axially relative to the outer gear 5056 and the wave generator5054 as the spring of the thrust bearing 5201 is compressed and thespring of the thrust bearing 5200 is extended.

The clutches may be selected from many suitable types, including conicalclutches, freewheels, viscous coupling, Hele-Shaw clutches, fluid drive,wet multi-plate clutch, epicyclical planetary gear system, wet clutch,magnetic inductance and other suitable.

Although not illustrated, a planetary gearbox can be used in place of aharmonic drive. Such a planetary box comprises a sun, a planet carrierand an annulus, wherein one of the sun, planet carrier and annulus isadapted to function as a rotary input component and another of the sun,planet carrier and annulus is adapted to function as a rotary outputcomponent in the downhole assembly of the invention.

These and other modifications and improvements may be incorporatedwithout departing from the scope of the present invention.

1. A downhole tool assembly, comprising: a first body and a second bodyarranged to rotate one relative to the other about a rotation axis and adrive arrangement between the first and the second body for rotating thefirst and the second body relative to each other, wherein the drivearrangement comprises a harmonic drive comprising a wave generator, aflexible gear and an outer gear, wherein one of the wave generator,flexible gear and outer gear is adapted to function as a rotary inputcomponent and another of the wave generator, flexible gear and outergear is adapted to function as a rotary output component; and whereinthe downhole tool assembly comprises at least one motor for rotating acomponent of the downhole tool assembly, wherein the harmonic drive isarranged in a couplable relationship with the motor so that rotation ofthe motor results in rotation of the first and the second bodiesrelative to each other.
 2. A downhole tool assembly as claimed in claim1, wherein the remaining one of the wave generator, flexible gear andouter gear is adapted to function as a stationary component of theharmonic drive.
 3. A downhole tool assembly as claimed in claim 1,wherein the downhole tool arrangement comprises a Bottom Hole Assembly(BHA) wherein at least one of the first and second bodies is included inthe BHA.
 4. A downhole tool assembly as claimed in claim 3, wherein thefirst and the second bodies have a common axis of rotation.
 5. Adownhole tool assembly as claimed in claim 4, wherein the motorcomprises a rotor component for driving the component of the downholetool assembly and a stator component wherein the rotary input componentof the harmonic drive is arranged in a couplable relationship with themotor so as to transmit rotation from the motor via the harmonic driveto the rotary output component of the harmonic drive.
 6. A downhole toolassembly as claimed in claim 5, wherein the rotary input component ofthe harmonic drive is arranged in a couplable relationship with therotor component of the motor so as to transmit rotation of the rotorcomponent of the motor via the harmonic drive to the rotary outputcomponent of the harmonic drive.
 7. A downhole tool assembly as claimedin claim 5, wherein the rotary input component of the harmonic drive isarranged in a couplable relationship with the stator component of themotor so as to permit the stator component of the motor to rotate underthe influence of reactive torque acting on the stator component duringrotation of the rotor component of the motor.
 8. A downhole toolassembly as claimed in claim 5, wherein a pair of harmonic drives isprovided, wherein in a first harmonic drive the rotary input componentis arranged in a couplable relationship with the rotor component of themotor so as to transmit rotation of the rotor component of the motor viathe harmonic drive to the rotary output component of the harmonic drive,and wherein the rotary input component of the second harmonic drive isarranged in a couplable relationship with the stator component of themotor so as to permit the stator component of the motor to rotate underthe influence of reactive torque acting on the stator component duringrotation of the rotor component of the motor and, wherein the firstharmonic drive is incorporated into the rotary output component of thesecond harmonic drive so that when the rotary output component of thesecond harmonic drive is rotated, the first harmonic drive rotates as aunit with the rotary output component of the second harmonic drive inthe direction opposite to the direction of rotation of the rotary outputcomponent of the first harmonic drive, thereby enabling rotation of therotary output component of the first harmonic drive in oppositedirections.
 9. A downhole tool assembly as claimed in claim 8, whereinone of the first and second bodies comprises one of the rotor componentor the stator component of the motor.
 10. A downhole tool assembly asclaimed in claim 9, wherein the motor is a downhole motor for rotating acomponent of the downhole tool, the downhole motor being arranged in apower section of the Bottom Hole Assembly (BHA) and wherein the rotorcomponent of the motor comprises a motor shaft extending substantiallycoaxially with the rotation axis of the first body relative to thesecond body and the stator component comprises a tubular motor housingwherein the housing encloses the motor shaft.
 11. A downhole toolassembly as claimed in claim 10, wherein the motor comprises a topmotorat surface wherein the rotor component of the motor comprises a drillpipe extending between the Bottom Hole Assembly (BHA) and the topmotor,wherein the harmonic drive is coupled to the drill pipe at the rotaryinput component and to the second body at the rotary output component.12. A downhole tool assembly as claimed in claim 11, wherein the firstbody comprises a drill pipe rotatable by a topmotor.
 13. A downhole toolassembly as claimed in claim 12 wherein the first body comprisesnon-rotatable coiled tubing.
 14. A downhole tool assembly as claimed inclaim 13, wherein the second body comprises a rotatable component of theBHA.
 15. A downhole tool assembly as claimed in claim 14, wherein theharmonic drive is connected between the motor shaft of downhole motorand the rotatable component of the BHA, so as to utilise the activetorque of the downhole motor to rotate the rotatable component of theBHA with reduction.
 16. A downhole tool assembly as claimed in claim 15,wherein the harmonic drive is coupled to the stator component of thedownhole motor and the stator component is coupled to the rotatablecomponent of the BHA so as to utilise the reactive torque acting on thestator component to rotate the rotatable component of the BHA.
 17. Adownhole tool assembly as claimed in claim 14, wherein the harmonicdrive is coupled between a drill pipe and the rotatable component of theBHA, wherein rotation of the drill pipe is transmitted to the rotatablecomponent of the BHA with reduction in order to orient a bent portion ofthe BHA or to allow the bent portion to rotate constantly butconsiderably slower than the drill pipe.
 18. A downhole tool assembly asclaimed in claim 17, wherein the harmonic drive is equipped with aclutch arrangement adapted for selective interruption of the rotaryconnection between the drill pipe and the BHA and/or for selectivelylocking the harmonic drive between the drill pipe and the BHA so thatthe drill pipe and the BHA rotate as one piece, and/or for alteringconnection sequence between the motor, the wave generator, the flexiblegear, the outer gear and the first or the second body of the BHA so thatthe first or the second body can be rotated in opposite directions. 19.A downhole tool assembly as claimed in claim 18, wherein the harmonicdrive is coupled between the motor and the first or the second body ofthe BHA, so that the first or the second body of the BHA is coupled witheither the flexible gear or the outer gear so that the first or thesecond body can be rotated in the desired direction, or a clutch meansis provided enabling first or the second body to be selectively coupledwith either the outer gear or the flexible gear, so that the first orthe second body can be rotated in opposite directions.
 20. A downholetool assembly as claimed in claim 19, wherein the outer gear is providedin the form of a stabiliser mounted around an outer circumference of thedownhole tool assembly
 21. A downhole tool assembly as claimed in claim20, wherein the stabiliser is a non-rotating stabiliser.
 22. A downholetool assembly as claimed in claim 21, wherein the outer gear is adaptedto function as a stationary component in the harmonic drive.
 23. Adownhole tool assembly as claimed in claim 22, wherein the outer gear isconfigured so that it remains stationary in a borehole due to frictionbetween the outer gear and a wall of the borehole while one of theflexible gear or the wave generator functions as the rotary inputcomponent.
 24. A downhole tool assembly as claimed in claim 23, whereinthe outer gear is configured so that the friction can be overcome whenthe outer gear is coupled to the motor to be rotated by the motor andthe harmonic drive is locked to rotate as a unit together with themotor.
 25. A downhole tool assembly as claimed in claim 24, wherein theouter gear is provided with a device which is configured to preventrotation of the outer gear in the direction opposite to the rotation ofthe outer gear when it is coupled to the motor and the harmonic drive islocked to rotate as a unit together with the motor, when the outer gearis required to remain stationary during the operation of the harmonicdrive, and permits rotation of the outer gear when the outer gear iscoupled to the motor and the harmonic drive is locked to rotate as aunit together with the motor.
 26. A downhole tool assembly as claimed inclaim 25, wherein the BHA is an orienting sub in which the relativerotation between the first body and the second body results in thechange of orientation of one of the two bodies with regard to the other,wherein the change in the orientation is angular, i.e. a change in therotational angle between the first and second bodies due to relativerotation of the first and second bodies about a common axis orlongitudinal, i.e. involving a change in the angle between longitudinalaxes of the first and the second bodies.
 27. A downhole tool assembly asclaimed in claim 26, wherein the BHA comprises a bent sub or a bentportion wherein the second body of the downhole tool assembly comprisesthe bent portion, wherein the bent portion has an axis positioned at anangle to a central axis of the downhole tool assembly, wherein rotationof the bent portion around the central axis of the downhole toolassembly results in a change of circumferential orientation of the bentsub.
 28. A downhole tool assembly as claimed in claim 27, wherein thebent portion or the bent sub is arranged so that the bend angle inrelation to the central axis of the downhole tool assembly can beadjusted downhole, wherein the bent portion comprises first and secondbend members, wherein the first bend member is co-axial with the centralaxis of the downhole tool assembly, and the second bend member isrotatably coupled to the first bend member and rotatable relativethereto about a second axis of rotation which is at a non-zero anglerelative to the central axis whereby the relative rotation of the firstand second bend members results in the change in the bend angle betweenthe bent portion and the central axis.
 29. A downhole tool assembly asclaimed in claim 28, wherein the harmonic drive comprises at least oneclutch arranged so as to selectively vary the transmission of rotationbetween the harmonic drive and the motor, so as to disable thetransmission or enable transmission of rotation with or withoutreduction and/or so as to change the direction of rotation at theoutput.
 30. A downhole tool assembly as claimed in claim 29, whereinactuating means is provided for selectively actuating the clutch.
 31. Adownhole tool assembly as claimed in claim 30, wherein the clutch isadapted to selectively alternately cooperate with one or more of thewave generator, the flexible gear and the outer gear so as to enable orrestrict rotation of that gear and so as to permit or restrict rotationof another gear, thereby enabling the change in the direction ofrotation to occur between the first and the second body.
 32. A downholetool assembly as claimed in claim 31, wherein the harmonic driveincludes one or more additional sets of an wave generator, a flexiblegear and an outer gear, wherein the additional set of gears is linked tothe existing set of gears so that the transmission ratio of the harmonicdrive is a product of the transmission ratios of the existing and theadditional sets.
 33. A downhole tool assembly as claimed in claim 32,wherein a torque limiting device is provided at the output of theharmonic drive in order to prevent components of the downhole assemblyfrom becoming damaged due to excessive torque.
 34. A downhole toolassembly as claimed in claim 10, wherein the harmonic drive is locatedabove the downhole motor, but within the BHA and is connected betweenthe drill pipe and a bent portion of the BHA so as selectively to permitthe rotation of the drill pipe from surface above the harmonic drivewhile minimising or preventing altogether rotation of the bent portion,wherein the reduction ratio of the harmonic drive is such that theresulting rotation of the bent sub is negligibly slow compared with therotation of the drill pipe that it can be regarded as non-existent. 35.A downhole tool assembly as claimed in claim 34, wherein the rotatablecomponent of the motor comprises an eccentric drive shaft of a downholemotor and the rotary input component of the harmonic drive is coupleddirectly to the eccentric drive shaft.
 36. A downhole tool assembly asclaimed in claim 35, wherein the downhole tool assembly forms part of adrill-string or work-string.
 37. A directional drilling tool,comprising: a first end attachable to a drillstring, and a second endattachable to a drill bit; a power section located intermediate thefirst and second ends, and adapted to provide power to the drill bit; aswivel section having first and second swivel members non-rotatablyattached to the first end and power section respectively, wherein thesecond swivel member is rotatably coupled to the first swivel member androtatable relative thereto about a first axis of rotation which isco-axial with a longitudinal axis of the tool; a first harmonic driveadapted to selectively rotate the second swivel member about the firstaxis of rotation; an adjustable bend section having first and secondbend members non-rotatably attached to the power section and the secondend respectively, wherein the first bend member is co-axial with thelongitudinal axis, and the second bend member is rotatably coupled tothe first bend member and having a second axis positionable at anon-zero angle relative to the longitudinal axis; and a second harmonicdrive adapted to selectively rotate the first and second bend membersrelative each other so as to vary the angle between the longitudinalaxis and the second axis.
 38. A directional drilling tool as claimed inclaim 37, wherein the drilling tool comprises a measurement whiledrilling (MWD) tool for reading and measuring drilling parametersinstalled below the swivel section and above the power section.
 39. Adirectional drilling system, comprising: a directional drilling tool ofclaim 37; a drill bit attached to the second end of the tool; ameasuring device adapted to monitor the orientation and position of thedrill bit; a remote control system having an operator control interfaceadapted to receive manual tool control inputs; and an electroniccontroller adapted to selectively activate the first and/or secondharmonic drives of the tool in response to signals from the measuringdevice and/or remote control system.
 40. A directional drilling system,as claimed in claim 39 wherein each of the swivel and adjustable bendsections comprise one or more positional sensors adapted to communicatethe rotational position of the swivel and adjustable bend sections tothe controller.
 41. A downhole tool assembly, comprising: a first bodyand a second body arranged to rotate one relative to the other about arotation axis and a drive arrangement between the first and the secondbody for rotating the first and the second body relative to each other,wherein the drive arrangement comprises a planetary gearbox comprising asun, a planet carrier and an annulus, wherein one of the sun, planetcarrier and annulus is adapted to function as a rotary input componentand another of the sun, planet carrier and annulus is adapted tofunction as a rotary output component; and wherein the downhole toolassembly comprises a motor for rotating a component of the downhole toolassembly, wherein the planetary gearbox is arranged in a couplablerelationship with the motor so that rotation of the motor results inrotation of the first and the second bodies relative to each other. 42.A directional drilling tool, comprising: a first end attachable to adrillstring, and a second end attachable to a drill bit; a power sectionlocated intermediate the first and second ends, and adapted to providepower to the drill bit; a swivel section having first and second swivelmembers non-rotatably attached to the first end and power sectionrespectively, wherein the second swivel member is rotatably coupled tothe first swivel member and rotatable relative thereto about a firstaxis of rotation which is co-axial with a longitudinal axis of the tool;a first planetary box adapted to selectively rotate the second swivelmember about the first axis of rotation; an adjustable bend sectionhaving first and second bend members non-rotatably attached to the powersection and the second end respectively, wherein the first bend memberis co-axial with the longitudinal axis, and the second bend member isrotatably coupled to the first bend member and having a second axiswhich is at a non-zero angle relative to the longitudinal axis; and asecond planetary box adapted to selectively rotate the first and secondbend members relative each other so as to vary the angle between thelongitudinal axis and the second axis.
 43. A directional drillingsystem, comprising: a directional drilling tool according to claim 42; adrill bit attached to the second end of the tool; a measuring deviceadapted to monitor the orientation and position of the drill bit; aremote control system having an operator control interface adapted toreceive manual tool control inputs; and an electronic controller adaptedto selectively activate the first and/or second planetary gearboxes ofthe tool in response to signals from the measuring device and/or remotecontrol system. 44.-46. (canceled)